Don’t take that hurricane season forecast to the bank

Hurricane season, mercifully, ends today. I had a story on it in the paper today, and I wanted to expound upon some of the research I did for the piece.

My general belief is that pre-season hurricane forecasts aren’t worth a whole lot. Why? Because there is simply no weather event that can be forecast, with precision, six months into the future. Therefore, the idea that you can predict there will be 15 named storms in a year seems a little ridiculous.

So I decided to calculate the average error over the last 7 years for Bill Gray and NOAA, the two most prominent forecasters. Why 7 years? Because that’s when NOAA began issuing numerical forecasts.

Here are the average annual errors I came up with, both including 2005, and, in parentheses, excluding 2005. I think it makes sense to exclude 2005 because it’s such an outlier that it’s not reflective of past accuracy rates.

Gray: 2.85 (1.5) named storms off

NOAA: 3.64 (2.2) named storms off

I figured that missing by nearly 4 storms probably wasn’t that great, especially since, between 1999 and 2004, the high number of storms was 16, and the low, 12. Pick the midpoint, 14, and you’d have a darn good forecast every season. So I essentially decided to do that.

To derive my forecast for any given year, I took the average number of named storms for the five previous years. For example, the 2002 forecast of 12.4 storms is based upon the average number of storms for the years 1997 to 2001. And it does a pretty good job. There were 12 named storms in 2002. Here are the average annual errors for SciGuy’s method:

SciGuy: 2.54 (1.2) named storms off

So, what does this tell us? That predicting hurricane seasons right now is still a lot of guesswork. It’s good for the news media — it gives us something to report, and meteorologists to blather about — but it’s not gospel. I have a lot of respect for Gray and NOAA, they’re doing interesting, inventive work, but it strikes me as something that’s a little like trying to build an atomic bomb without fully understanding the principle of fission.

One other peeve about NOAA’s forecast: During a teleconference yesterday they were bragging that they hit the mark with their May forecast by saying, at the time, there was a 70 percent chance of having an above average season in 2005.

What value is there in such a prediction? Because of the multi-decadal oscillation in Atlantic Sea Surface temperatures, we’re in an active period for hurricanes. During such a period, at least 70 percent of years will be above average in terms of named storms forming.

Therefore, predicting a 70 percent chance of an “above-average” season in this era is the equivalent, in my mind, of saying that a land-falling category-5 storm has a 70 percent chance of doing bad things to a home near the coast.

11 Responses

Eric–very interesting work. You undoubtedly realize the dangers inherent in extrapolating from past weather trends to predict the future. As an example, consider tornadoes. According to NOAA records, my former hometown of Wichita Falls and the surrounding county were hit by an average of one or more tornadoes almost every year between 1950 and 1979, including three violent tornadoes that struck the city itself (an F3, an F4, and an F5). You might predict from those figures that the area would continue to be hit at least every few years in the future. However, in the entire decade of the 1980s, the county recorded only one weak tornado strike, and no tornadoes hit the city. There were a handful of weak tornadoes during the 1990s, all occurring in rural areas, and then finally there was a direct hit on the city in 2002 by another weak storm (right on top of my old neighborhood). An entire generation of Wichitans has grown up thinking that Wichita Falls never has tornadoes–even the local newspaper has managed to forget the past and recently tried to claim that the city lies in some kind of “protected zone” in the middle of Tornado Alley. My own prediction is that they’re long overdue for another destructive tornado, and that a lot of people aren’t going to know what to do to protect themselves. Anybody care to lay odds?

Of course there are dangers in extrapolating from past weather trends; weather is inherently unstable and unpredictable. That was my point in respect to the pros making hurricane season forecasts. I found it pretty fascinating that simple climatology, at least in the near term, was a better predictor.

Your tornado hypothesis is an interesting one. As you’ll recall, I posted some stuff about tornadoes about a month ago (http://blogs.chron.com/sciguy/archives/2005/10/cool_stuff_abou.html). The coolest fact I found is that you’re likely to get hit — at your home — by an F2 or greater tornado in Houston once every 5,000 to 10,000 years.

But let’s not talk about tornadoes so soon after the WORST hurricane season ever. It’s the year of the hurricane, OK? I’d hate to think about piling a destructive tornado on top of that…

OK–for now! Your predictions are pretty good, retroactively. Maybe next season you can be the voice of reason when the superheated media coverage starts back up upon the appearance of the first tropical storm (assuming they don’t keep appearing all winter long.) Many ancient scientists assumed that there were links between astronomical phenomena and weather events. You’re an astronomer–we’ll find out if the ancients were right!

Interestingly, the Houston Weather Research Center’s seasonal forecast is based on a 13-year solar cycle — so even some of the modern scientists look to the heavens for answers to weather phenomena here on Earth.

Oh, great..I move out of the Hurricane Zone, and into drought, ice storms, wild fires and Scott wants to remind me that now I’m in Tornado Alley!

I lived near Wichita Falls, In Electra, (30 miles from the Falls) for a short period of time, thank God, and the sense to leave. In the main, the town’s nightly entertainment during tornadic activity season, (9 months of the year) consisted

of training the town-owned spotlight, in the town square, into the swirling clouds overhead! If bad things were seen, then everyone scurried home to their storm shelter!

My very young children and I were caught, in a car directly in the path of the 1957 Dallas tornado. We managed to get away from it, applying the little knowledge I’d gained in west Texas.

The 1999 Oklahoma City disaster caused much anxiety, as the Company for which I worked had a facility there, and we KNEW all those people. Thankfully, the damage at our plant was confined to property, and displaced, but didn’t injure our personnel.

However, I still like Hurricanes somewhat less than tornadoes…as I remarked in a different post awhile back, the tornado usually kills quickly, moves on, and doesn’t drown you slowly.

I realize that tornadoes sometimes create a wide swath of destruction, leave years of devastion behind, but they rarely impact as wide an area, and thousands of people for months and years to come. I’d really like not to get caught in either.

However, watching the suffering on TV (I couldn’t not watch) during and after Katrina, when my friends were in the disaster zone, was trauma

enough for me. It may have also saved my life. When the mayor of Lake Charles, La. said the words, “mandatory evacuation”, the little dogs and I got into an already packed car, and LEFT!

I have some regrets for the life we left behind, and miss friends, neighbors and family members,

When I lived in the San Francisco bay area in the early 90′s, one of the local newspapers did a study of the accuracy of the local weather forecasts. It is my recollection that they concluded that the accuracy, averaged over about a year, would have been improved a bit if they had replaced the forecast each night with the sentence “it will be the same tomorrow as it was today.”

But that would put many a handsome weatherman out of a job, now wouldn’t it?

Dan, don’t forget all the beautiful TV weather-women who would also lose their jobs. (g) It’s interesting to note that in the early days of TV, physical attractiveness was not a requirement for television meteorologists like it is now. Harold Taft, who was the chief meteorologist on WBAP-TV in Fort Worth from the station’s first sign-on in 1948 until his death in 1991, looked like a beat-up old ranch hand (not unlike his boss, Amon Carter), but he was revered by local viewers for his plain-spoken accuracy about the weather. Even now, WBAP’s successor station, KXAS-TV, continues to beat its Dallas competitors in severe weather coverage. Sadly, Taft probably wouldn’t be able to get a job on TV today because he didn’t have enough hair left to blow-dry in the shape of a football helmet.

Scott: Neither Harold Taft, nor his successor, David Finfrock (who has lots of hair, though it is greying a bit now,) would be caught dead hanging on to a lamp post during a hurricane or tornado!

“The Bow-tie Guy” had two combed-over wisps when he started doing weather All attempts by management to make him more personable and less arrogant failed, even putting him on a corner in a red-bow tie, mike in hand, accepting charitable donations to children at Christmas. Or, at least it failed with me!